The present disclosure relates generally to semiconductor manufacturing. Specifically, the present disclosure relates to fabricating a microstructure device with an improved anchor having a reduced undercut.
The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component that can be created using a fabrication process) has decreased.
Microelectromechanical systems (MEMS) devices are very small electro-mechanical systems incorporated into semiconductor IC circuits. One example of a MEMS device is a micro-inertial sensor/accelerometer. Conventional silicon on insulator (SOI) type MEMS devices are fabricated using a buried oxide layer as a sacrificial material layer. As such, a portion of the oxide layer is removed at a later stage of fabrication to release the MEMS device. Generally, the amount of oxide to be removed is time controlled where the etch time depends on the physical dimensions of the MEMS device. Because the oxide etches uniformly, the oxide is removed both from under the MEMS device and laterally from under supporting structure, such as the anchor. This causes an undercut problem for the anchor, which can weaken the anchor. The etching is usually performed from outside edges of the MEMS device and thus, the undercut of the anchor is approximately half of the dimension of the MEMS device. The undercut reduces strength of the anchor. To combat this large undercut problem, designers may perform an etch process of the oxide layer through the MEMS device using a number of release holes/trenches through the MEMS device to allow the etchant to etch the oxide layer beneath the MEMS device more quickly by etching from multiple areas. However, this type of etching compromises the MEMS device by limiting device design flexibility and degrading device performance (e.g., reducing total mass of a MEMS accelerometer).
Therefore, what is needed is a system of fabricating a microstructure device with an improved anchor.